The present invention relates to a mechanical acceleration sensor for activating a gas generator of an inflator in an air bag system or a pretensioner in a seat belt system.
Vehicles, for example, automobiles, are often provided with an air bag system or a seat belt system or both. For an inflator in the air bag system or a pretensioner in the seat belt system, a gas generator is employed as a device of generating a driving medium for the inflator or the pretensioner. Such a gas generator is activated by an acceleration sensor. As an acceleration sensor, a sensor that outputs an electric signal has heretofore commonly been used because this type of sensor is superior in acceleration pulse discriminating ability and hence advantageous in that an erroneous operation is unlikely to occur. However, electrical sensors have the disadvantage of having limitations on the locations of installation, because they require a power supply and electrical connection. Accordingly, various proposals have heretofore been made with regard to a mechanical sensor, which needs no electric supply or electrical connection, can be located in places where it is difficult and costly to install an electrical sensor, and can be constructed at a relatively low cost.
One form of mechanical sensor, which is disclosed in U.S. Pat. No. 4,955,638 has a weight, a trigger lever and a firing pin, which are movably supported in a sensor casing. When a predetermined level of acceleration occurs and acts on the weight, the trigger lever is activated by inertial movement of the weight, causing the spring-loaded firing pin to perform a percussive action, thereby firing a percussion cap attached to a gas generator.
In the mechanical sensors which have heretofore been proposed, including the above-described sensor, various studies have been pursued with regard to the sensor function. However, insufficient consideration has been given comprehensively to such matters as simplification of the arrangement, reduction in the number of parts required, and improvements in the manufacturing and assembling procedures.